1. Field of the Invention
The present invention relates to mechanical working of metals and more in particular to hydraulic presses.
This invention can advantageously be used for the manufacture of fast-acting hydraulic presses effective for punching sheet materials through elastic, hydroelastic (through fluid via elastic diaphragm), and fluid media. In addition, this invention can find application in the manufacture of pneumatic percussion press installations.
2. Description of the Prior Art
There is known in the art a hydropunch which comprises a cylinder with a ram movably mounted therein. The ram is forced down by compressed gas to strike against an elastic medium contained in the working chamber, thus creating high pressure therein effecting the deformation of the workpiece. In order to avoid an excessive increase of pressure inside the cylinder in the interspace between the ram and the elastic medium (fluid), and to prevent kinetic energy of the ram from being absorbed by air cushion, the part of the cylinder chamber disposed before the elastic medium is communicated with the atmosphere through outlet ducts.
However, it is rather problematic to return the ram to its original position on completion of its operating stroke.
There is known, for example, a hydropunch wherein the ram is raised to its original position by means of working fluid passing from a hydraulic drive under the ram. Once the ram is up, the fluid is to be removed from the cylinder, for example, by means of blowing air therethrough. Therefore, the hydraulic system as a whole is rendered cumbersome by an excessive number of various controlling, regulating and distributing devices, as well as pumps, pipelines and other auxiliary components provided therein. The time period required for ram-raising-, air-blowing, and fluid-draining operations is 50 to 60 sec., French Pat. No. 1,562,426.
In other known hydropunches (cf. The article "High-Speed Working by Hydropunch Method", Ratjen R., Takamatsu M., Express Information Bulletin No. 21, 1971, series "Forging and Pressing Production Technology and Equipment)", with the ram impact on the fluid, the above-the-ram chamber of the cylinder is successively brought into communication, through respective valves, with a compressed gas receiver, with the atmosphere and, finally, with the vacuum receiver. Therefore, the operations undertaken to return the ram to its original position are disadvantageous in that they increase the time period of the operating cycle. Furthermore, the provision of valves, pipelines and receivers makes the hydropunch more complicated and expensive in construction.
There is also known an apparatus for establishing hydraulic impact load (cf. French Pat. No. 2,138,378), which comprises a cylinder with a stepped ram, a chamber intended for a water diaphragm to be formed therein which chamber is positioned before the cylinder and is separated therefrom by a partition with an opening in its centre to receive the ram. The partition is also provided with a plurality of holes facing recesses formed in the ram, through which air is passed to effect return stroke of the ram; a headpiece for supplying water required to form the diaphragm; a water outlet and an air vent hole; an air supply regulating valve; an additional air distributor; a gate; a return stroke distributor; a valve for stopping the ram on its return stroke; a duct-and-pipeline system.
In the aforedescribed apparatus a means for returning the ram to its original position comprises a return-stroke control valve, a duct intended to communicate the directional control valve with the cylinder, a duct with a valve, intended for the passage of air fed through the control valve under the ram, and a duct communicating the above-the-ram chamber of the cylinder, through control valve with the atmosphere. The ram is returned to its original position in the following manner.
When the downwardly moving ram reaches the water diaphragm, the ram accelerating air passes through a duct and thus causes displacement of the return-stroke control valve plunger, thereby communicating the above-the-ram chamber of the cylinder with the atmosphere. As a result, the air pressure is brought down in the cylinder. At the same time, the air from the receiver is admitted beneath the ram, thereby initiating its return stroke. As pressure drops in the cylinder, the spring-actuated plunger of the control valve is returned to its original position, thereby discommunicating the above-the-ram chamber of the cylinder and stopping the supply of air under the ram. On having gained speed, the ram continues its movement by inertia, and at the end of its return stroke it is cushioned by the air present in the above-the-ram chamber of the cylinder.
However, the apparatus described above is not free from disadvantages, the most serious of which is complexity of its construction which, in turn, may bring about failures in operation. All compressed gas control valves of the type described above are known to suffer from gas leakage due to occur through gaps in the housing-and-valve assembly. In order to preclude leakage in air control valves, the size of gaps in the housing-and-valve assembly should be minimized (a gapless assembly would be ideal), and the presence of moisture in the air makes it imperative to manufacture them from corrosion-resistant materials. In addition, these types of control valves require that the air be thoroughly cleaned of solid impurities and a lubricant oil be well pulverised to provide for effective lubrication of the surfaces subject to friction.
Other disadvantages of the prior-art apparatus lie in that it requires a high flow rate of air to be admitted beneath the ram so as to initiate its return stroke. As the ram is returned to its original position, it strikes against the traction rod of the auxiliary control valve, thereby shortening the service life of the latter.
Still another disadvantage of the prior-art apparatus is the absence of means required for retaining the ram in its original position, which may result in failure to actuate the ram. From the above it follows that the aforedescribed apparatus (inclusive of the means for returning the ram) is operable if furnished with a stepped ram. In other words, the ram mass per unit of the cylinder area (specific mass), wherein impact load is created, will be substantial. However, the ram with a minimum specific mass is known to be more effective for such operations as shaping rigid reliefs, coining and sizing. This being the case, the process in the chamber is similar to a shock-wave process, which is characterized by an extremely high pressure on the wave front, whereas in the event of a big specific mass of the ram, the process in the chamber is more of a static nature (quasistatic). For the aforesaid operations efficiency of the energy transfer from the fluid, with a high impulsive pressure established therein, to the work-piece is considerably higher when the transfer of energy is effected in the form of a shock wave than through the intermediary of quasistatic pressure.
The principal object of the invention is to provide a hydropunch for use in a press which will be more simple in construction and reliable in operation than similar arrangements known in the art.
Another object of the invention is to provide a hydropunch which will have higher efficiency than the prior-art arrangements of similar type.
Still another object of the invention is to provide a hydropunch of the type to permit a faster return of the ram to its original position and reliable fixing thereof in this position.
Yet another important object of the invention is to provide a hydropunch of the type permitting both the travelling path and leakage of air to be reduced during working and return strokes of the ram.
Another object of the invention is to provide a hydropunch which will ensure a reliable return of the ram to its original position in the event of using a fluid as the working medium while subjecting workpieces to large amounts of deformation.
These and other objects of the invention are attained in a hydropunch for use in a press including a die on the working surface of which is placed a piece to be worked, comprising a cylinder having a wall body with two ends, one of which faces the working surface of the die, the other looking in the opposite direction therefrom; a ram accommodated within said cylinder with a possibility to move therealong so as to form therein an above-the-ram chamber and a below-the-ram chamber; a means for actuating said ram, said means being arranged on the opposite end of said cylinder; a compressed gas receiver communicating with the above-the-ram chamber; a cover intended for closing both said cylinder and receiver; a means for returning the ram to its original position, said means including a closed chamber communicating with the below-the-ram chamber of said cylinder, and a valve adapted to communicate the above-the-ram chamber of said cylinder with the atmosphere.
Such construction of the means for returning the ram to its original position makes it possible to eliminate the valve-and-pipeline system, thereby ensuring, on the one hand, a simple and reliable construction and, on the other, precluding leakage of compressed gas through the gaps in the slide valve, and loss of energy due to occur during the passage of gas through pipelines.
It is advantageous to utilize used compressed gas to ensure a faster return of the ram and its reliable fixing in a collet. To this end, a non-return valve, intended for admitting the used gas to the closed chamber, is preferably built in the wall of the cylinder at a distance from the end thereof facing the die, approximately equal to the height of the ram.
It is also preferred to have the closed chamber arranged concentrically with the cylinder at the end thereof facing the die, and to have this chamber connected through ducts with the below-the-ram chamber of the cylinder. This will reduce both the travelling path and leakage of air on its way from the below-the-ram chamber to the closed chamber during the operating and return strokes of the ram.
To render the ducts more simple in construction and shorter in length, the valve can be accommodated in the opening, provided for this purpose in the cover, so as to communicate the above-the-ram-chamber with the atmosphere. The construction is simplified by means of the cover used as the body for both the valve and ducts formed therein, which makes unnecessary the use of pipelines.
To ensure a reliable return of the ram, it is advantageous to provide a non-return valve through which compressed gas is admitted under the ram and into a chamber which is to be filled with a fluid in the event of using it as the working medium while working pieces which require substantial amount of reduction.